Single-Carrier Signal Crest Factor Reduction via Iterative Clipping
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Solution Overview
Problem
Current techniques fail to effectively reduce the crest factor of single-carrier modulations in radio transmission equipment for 4G LTE uplink without degrading the signal spectrum or impacting bit error rate, particularly in SC-FDMA signals with high PAPR.
Innovation Solution
A method and device that utilize a return chain for clipping, filtering, and demodulation of the signal, followed by symbol modification to generate modified symbols that reduce the crest factor while maintaining spectral compliance, using techniques like deep clipping and iterative processing to achieve a lower PAPR without degrading performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If clipping is applied to reduce PAPR, then power amplifier efficiency is improved, but signal spectrum is degraded
Solution Approach 1:
The patent implements an iterative feedback mechanism where the clipped signal is demodulated, the modified symbols are determined based on the demodulated signal and initial symbols, and the process repeats with modified clipping thresholds. This feedback loop allows the system to learn from each iteration and adjust the clipping level to minimize spectrum degradation while maintaining PAPR reduction benefits.
Solution Approach 2:
The patent performs preliminary actions by determining modified symbols before final signal transmission. The system pre-processes the clipped signal through demodulation and symbol modification, preparing corrected symbol sequences that will be used in subsequent iterations or final signal generation, thereby preventing spectrum degradation before it occurs.
2Ease of operation
If iterative processing is used to reduce PAPR, then crest factor reduction is improved, but device complexity increases
Solution Approach 1:
The patent employs dynamic iteration where the number of processing iterations is not fixed but adapts based on convergence criteria. The system can dynamically adjust the clipping threshold and modify symbols iteratively, allowing the processing complexity to scale with the required PAPR reduction level rather than applying maximum processing in all cases.
Solution Approach 2:
The patent applies local quality by selectively modifying only those symbols that contribute most to PAPR degradation. Instead of uniformly processing all symbols through complex iterative algorithms, the system identifies and modifies specific problematic symbols based on their contribution to the crest factor, reducing overall processing complexity while maintaining effectiveness.
Data Source
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Figure 3a~3b
AI summary
A method for reducing the crest factor in a device for emitting a single-carrier signal, characterized in that it comprises: • a step of grouping symbols to be emitted into blocks, and for each of the blocks of symbols: o a second step of generating (103, 110) a single-carrier signal from said block of symbols, o a third step of clipping (120) said single-carrier signal, o a fourth step of generating (130, 104) clipped symbols from said clipped single-carrier signal, o a fifth step of generating (106) a block of modified symbols from said block of symbols of the first step, said block of symbols clipped during the fourth step, and a modulation constraint, o a sixth step of generating and transmitting a single-carrier signal from said block of modified symbols.